AARRGGHHH! 1978 70hp

[fireman57]

I think I am about give up. Engine gets up and goes okay but after 20-30 seconds at WOT starts to lope and run lean. I can squeeze the bulb and keep it going. I know that sounds like fuel pump so put a brand new one on. The pulse from the crankcase is strong. I'm 99% sure it is an air leak somewhere. Thought I had it isolated to the carb body being worn where the throttle butterflies go through. Put some heavy grease on them and it ran fine for a half an hour. Took it out today and the same things started up. New grease and same thing. The fuel filter stayed full when it was running fine but now looks almost empty. Cannot keep it full by priming the bulb now as the bulb stays firm.
So far:
Compression is 125lbs on all three cylinders
Carbs rebuilt and perfectly clean
New fuel pump.
New alcohol resistent fuel and vacuum lines on engine
Tested on a known good tank.

The only difference in yesterday when it was running good and today is that we adjusted the idle down on the water.

doing a search on this engine here has revealed that it seems to be a common problem with '76-'80 models. Haven't found many threads where the problem has been solved.

Joe Reeves and Dhadley have helped but I still can't figure it out.

I'm just about ready to throw in the towel but it is such a strong engine.

 

[Will Bark]

Re: AARRGGHHH! 1978 70hp

Two things come to mind; tank vent fully open and o-ring in fuel line connector at the engine.

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

tank is vented. Even had cap off. Bypassed connector and ran straight to fuel pump. Whoever figures this out wins the grand prize.

 

[Will Bark]

Re: AARRGGHHH! 1978 70hp

Faulty primer bulb valves?

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

Can't be. Tried it on a known good tank. has to be an air leak somewhere as far as I can tell.

 

[tx1961whaler]

Re: AARRGGHHH! 1978 70hp

Cannot keep it full by priming the bulb now as the bulb stays firm.

Investigate this further. Also when you say "known good tank" do you mean known good tank and fuel line and bulb?

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

yes, known good tank, primer bulb, and line.

 

[Will Bark]

Re: AARRGGHHH! 1978 70hp

Try setting your float drop to the maximum about 1- 1/2 inches and see if it keeps running @ WOT; I know you set the float level even with carb body upside down. I had to do that on one of my engines before she would keep running.

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

There are three of them and I can't imagine just one of them not letting in enough gas but it's worth a try. I can pump the primer bulb to keep it going but I have to pump like a madman. It is also staying hard now where it used to soften up.

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

bump

 

[willamettejeff]

Re: AARRGGHHH! 1978 70hp

Fireman, what your motor doing at WOT? Does it seem like all 3 cylinders just want to quit at the same time? I have the same motor on my boat and had a similar problem when I first got it. Would run great when was cold for about 30 - 45 minutes, then stumble at WOT with all 3 cylinders quitting together. Would run at lower speeds for a time, but rough and couldn't accelerate above 3000, then 2000 without the motor quitting. Since you've done all the fuel stuff and not solved the problem it might be time to look at something else. On mine it turned out to be the powerpack that had developed a heat related problem and was crossing up the spark between the 3 cylinders. Replacing it fixed the problem and worked fine thereafter for many years. Just a thought since you've done everything else with the fuel system and I've seen where a failing powerpack can look like fuel problems. I have a good one I could send you if you would like to just try it. A few years ago I converted my 1978 70hp Johnson over to the more available, more modular, and less expensive 1989 ignition components I purchased off of Ebay that were from a 1989 60hp Evinrude. Did a complete swap over including the stator and timing sensor, so I have all the original 1978 ignition system components even the mounting bracket just sitting around in my garage. Really wasn't at all necessary, but that is just how I am (a tinkerer that just can't leave anything alone). Just PM me and we can work out the details if you would like to give it a try and if it fixes your problem then I expect to receive that "grand prize" you spoke of.

-- Jeff

 

[durban]

Re: AARRGGHHH! 1978 70hp

if the timer base & stator & power pack don't fix it , then you left with water coming into the ports or port ,

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

Jeff it doesn't just quit but lopes because it is starving for fuel. Spark is still good at WFO so it is not a powerpack or coil issue.
durban we did have water in #2 cylinder but head gasket and port side exhaust gaskets took care of that. Screwing around with it last night revealed bubbles in the fuel pump outlet so will experiment with a straight line to the gas tank today. Btw, I get a kick out of reading your theories. Keep up the good work.

 

[willamettejeff]

Re: AARRGGHHH! 1978 70hp

OK then Fireman. Offer still good as long as I still have the parts should you get to that point. Really hope you get it fixed. I just love the old Johnson/Evinrude 70 horse motors and a little SeaFoam in with each fill-up keeps mine running just great.

-- Jeff

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

Really appreciate it. Hopefully won't ever need them but good to know where some are. We'll get it figured out somehow.

 

[fireman57]

Re: AARRGGHHH! 1978 70hp

Well it turned out to be a combination of problems. bubbles were from a bad pickup tube in one tank and now loosing spark on a cylinder. Jeff you have a pm.